Web Hosting Tutorials

Email account disk usage incorrect

Posted on December 29th, 2006 by Alex P..
Categories: Cpanel Hosting, web Hosting, EXIM, VPS / OpenVZ.

Greetings ,

You can use the following command to remove the belows files from all users account on server.

find /home/*/.cpanel-datastore/ -name “diskusage_*” | xargs rm -f
find /home/*/mail/ -name maildirsize | xargs rm -f

Alex

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What is Spam Assassin and How it is work ?

Posted on December 26th, 2006 by Alex P..
Categories: Cpanel Hosting, Linux, web Hosting, EXIM, VPS / OpenVZ.

What is Spam Assassin ?
The SpamAssassin system is software for analyzing email messages, determining how likely they are to be spam, and reporting its conclusions. It is a rule-based system that compares different parts of email messages with a large set of rules. Each rule adds or removes points from a message’s spam score. A message with a high enough score is reported to be spam.
Spam Assassin is a e-mail spam filtering system that sits side by side with account with us to help block, mark or filter out mail you don’t want.

How do I access Spam Assassin?
First thing you will want to do is log into your cPanel. From there, under the “Mail” box look at the nine a link that reads “Spam Assassin”. From here it will tell you if Spam Assassin is currently enabled or disabled. Clicking the boxes to enable or disable Spam Assassin is how you can turn it on or off. To configure the Spam Assassin settings click the button that reads: “Configure Spam Assassin (required to rewrite subjects)”

How do I configure Spam Assassin?
If you do not know what it is you are looking at, the next screen could be a little confusing. To help you understand here’s a break down of what you should see on the screen and what do do with it:

required_hits - The number of e-mails received before marked as spam.
rewrite_subject - The tells Spam Assassin if it should rewrite your subject line or not as you define. (1 is yes and 0 is no)
subject_tag - What the spam is marked with in the subject line. (usually ***SPAM*** or something else that could be picked up by your own mail filters on your mail client of choice)
blacklist_from - An e-mail address you definitely want to be marked as spam. (you could also use *@something.com to get every email from that address filtered)
whitelist_from - An e-mail address you definitely do NOT want to be marked as spam. (you could also use *@something.com to get every email from that address NOT filtered)

Once you’re done, just hit save and whatever you defined on the earlier page will now be in effect. If you picked to rewrite the subject, then you could now go into your mail client and write a new “rule” that would filter all mail with “***SPAM***” to go into a SPAM folder so that you could check it from time to time making sure you did not get any false positives.

How do I use the Spam Box ?
You can turn your spam box enable and disable from the same page as Spam Assassin. It’s just that easy! With the recent upgrades to cPanel, the TotalChoice Hosting team has been paying more attention to the users of Spam Assassin.

In the previous build you would need to use a imap client to get to your spam box.
Well not anymore. You can create a “new” e-mail account that has precisely the same settings as your e-mail account, but add: “/spam” to the end of the e-mail account user name. This will retrieve only your Spam Box mail.

In order for this to be useful, you will want to set up your e-mail client to deliver this Spam Box mail to a special folder (perhaps called spam?) automatically.

How spamassassin works

Check out its feature on how it works.

–> There are several ways that SpamAssassin makes up its mind about a
message:
–> The message headers can be checked for consistency and adherence to
Internet standards (e.g., is the date formatted properly?).
–> The headers and body can be checked for phrases or message elements
commonly found in spam (e.g., “MAKE MONEY FAST” or instructions on how to be
removed from future mailings)-in several languages.
–> The headers and body can be looked up in several online databases that
track message checksums of verified spam messages.
–> The sending system’s IP address can be looked up in several online lists
of sites that have been used by spammers or are otherwise suspicious.
–> Specific addresses, hosts, or domains can be blacklisted or whitelisted.
A whitelist can be automatically constructed based on the sender’s past
history of messages.
–> SpamAssassin can be trained to recognize the types of spam that you
receive by learning from a set of messages that you consider spam and a set
that you consider non-spam. (SpamAssassin and the spam-filtering community
often refer to non-spam messages as ham. )
–> The sending system’s IP address can be compared to the sender’s domain
name using the Sender Policy Framework (SPF) protocol (http://spf.pobox.com)
to determine if that system is permitted to send messages from users at that
domain. This feature requires SpamAssassin 3.0.
–> SpamAssassin can privilege senders who are willing to expend some extra
computational power in the form of Hashcash (http://www.hashcash.org).
Spammers cannot do these computations and still send out huge amounts of
mail rapidly. This feature requires SpamAssassin 3.0.

Most of SpamAssassin’s behavior is controlled through a systemwide
configuration file and a set of per-user configuration files. The per-user
configuration can also be stored in an SQL database.

How to Configure it ? : -
——————-

You can easily customize how SpamAssassin tags and identifies spam by
creating a spamassassin/user_prefs file. You can customize the number of
“spam points” required to identify a message as spam, create new rules, and
re-weight existing rules. Here is a sample user_prefs file. It raises the
threshold for identifying spam from 5 to 6, disables including spam warnings
in the subject and body, reweights a known rule, and adds several blacklist,
whitelist, and header rules.

Listing 1. A typical user_prefs configuration file

================================================================

#How many hits before a mail is considered spam?
required_hits 6

#Don’t mangle the messages so badly
rewrite_subject 0
use_terse_report 1

#whitelist and blacklist
whitelist_from *@www.sgugal.com
blacklist_from annoying-person@xyz.com

#reweight an existing rule
score BASE64_ENC_TEXT 3

#add some new rules
header KNOWN_LIST List-Id =~ /a-mailing-list-i-like/
score KNOWN_LIST -3

body EVITE /This invitation was sent to you by .* using Evite/
describe EVITE Looks like an eVite
score EVITE -3

Alex

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Learn about SOA records

Posted on December 26th, 2006 by Alex P..
Categories: Cpanel Hosting, Linux, web Hosting, VPS / OpenVZ.

To an Administrator, there is nothing more peaceful than a stable and optimized DNS server. The moment there is a wrong configuration, the server wakes up and starts crying, sites and email goes down. An important part of keeping DNS that way is properly setting up the SOA records.

What are DNS Records. DNS records or Zone files are used for mapping URLs to an IPs. Located on servers called the DNS servers, these records are typically the connection of your website with the outside world. Requests for your website are forwarded to your DNS servers and then get pointed to the WebServers that serve the website or to Email servers that handle the incoming email.

This is how a typical Zone file (containing many common DNS records) looks like.

; Zone file for sgugal.com.

@       86400 IN SOA ns1.sgugal.com.   root.manou.sgugal.com. (

2006061904

86000

7200

3600000

86400 )

sgugal.com. NS IN 86400 ns1.sgugal.com.

sgugal.com. NS IN 86400 ns2.sgugal.com.

sgugal.com. 14400 IN A 69.20.54.201

localhost. sgugal.com. 14400 IN A 127.0.0.1

sgugal.com. 14400 IN MX 0 sgugal.com.

mail 14400 IN CNAME sgugal.com.

www 14400 IN CNAME sgugal.com.

ftp 14400 IN CNAME sgugal.com.

SOA Records

An SOA(State of Authority) Record is the most essential part of a Zone file. The SOA record is a way for the Domain Administrator to give out simple information about the domain like, how often it is updated, when it was last updated, when to check back for more info, what is the admins email address and so on. A Zone file can contain only one SOA Record.

A properly optimized and updated SOA record can reduce bandwidth between nameservers, increase the speed of website access and ensure the site is alive even when the primary DNS server is down.

Here is the SOA record. Notice the starting bracket “(“. This has to be on the same line, otherwise the record gets broken.

; name TTL class rr Nameserver email-address

@ 86400 IN SOA ns1.sgugal.com. root.linux5.nettoolz.net. (

2006061904 ; Serial number

86000 ; Refresh rate in seconds

7200 ; Update Retry in seconds

3600000 ; Expiry in seconds

86400 ; minimum in seconds )

• name - mydomain.com is the main name in this zone.

• TTL - 86400 - TTL defines the duration in seconds that the record may be cached by client side programs. If it is set as 0, it indicates that the record should not be cached. The range is defined to be between 0 to 2147483647 (close to 68 years !)

• Class - IN - The class shows the type of record. IN equates to Internet. Other options are all historic. So as long as your DNS is on the Internet or Intranet, you must use IN.

• Nameserver - ns.nameserver.com. -The nameserver is the server which holds the zone files. It can be either an external server in which case, the entire domain name must be specified followed by a dot. In case it is defined in this zone file, then it can be written as “ns’’ .

• Email address – root.linux5.nettoolz.net. -This is the email of the domain name administrator. Now, this is really confusing, because people expect an @ to be in an email address. However in this case, email is sent to [EMAIL=”root@ns.nameserver.com”] root@ns.nameserver.com[/EMAIL], but written as root.ns.nameserver.com . And yes, remember to put the dot behind the domain name.

• Serial number - 2006061904 - This is a sort of a revision numbering system to show the changes made to the DNS Zone. This number has to increment, whenever any change is made to the Zone file. The standard convention is to use the date of update YYYYMMDDnn, where nn is a revision number in case more than one updates are done in a day. So if the first update done today would be 2006061904 and second update would be 2006061905.

• Refresh - 86000 - This is time(in seconds) when the slave DNS server will refresh from the master. This value represents how often a secondary will poll the primary server to see if the serial number for the zone has increased (so it knows to request a new copy of the data for the zone). It can be written as “23h88M’’ indicating 23 hours and 88 minutes. If you have a regular Internet server, you can keep it between 6 to 24 hours.

• Retry - 7200 - Now assume that a slave tried to contact the master server and failed to contact it because it was down. The Retry value (time in seconds) will tell it when to get back. This value is not very important and can be a fraction of the refresh value.

• Expiry - 3600000 - This is the time (in seconds) that a slave server will keep a cached zone file as valid, if it can’t contact the primary server. If this value were set to say 2 weeks ( in seconds), what it means is that a slave would still be able to give out domain information from its cached zone file for 2 weeks, without anyone knowing the difference. The recommended value is between 2 to 4 weeks.

• Minimum - 86400 - This is the default time(in seconds) that the slave servers should cache the Zone file. This is the most important time field in the SOA Record. If your DNS information keeps changing, keep it down to a day or less. Otherwise if your DNS record doesn’t change regularly, step it up between 1 to 5 days. The benefit of keeping this value high, is that your website speeds increase drastically as a result of reduced lookups. Caching servers around the globe would cache your records and this improves site performance.

Increasing site speed

The time it takes to access a website on a browser includes the time it takes to look it up on the domain name server. By increasing the “Minimum’’ value, we’re telling the contacting clients to keep their copies of the zone file for a longer time. In effect, reducing the lookups to the nameserver. By reducing the number of times a client has to lookup, we’re increasing the site speed.

However, this also means that if you make changes to the DNS record, it will take longer to propagate. If you require to make frequent updates to your DNS records, make sure your Minimum value is lesser than 1 day. That means longer lookup times, but accurate information for the clients

If you are planning a major update on the DNS zone file(say moving to another server or hosting service), reduce the Minimum value a couple of days prior to the change. Then make the change and then jack up the minimum value again. This way the caching clients all over the world will pick up the changes quicker and yet you do not need to sacrifice on site speed thereafter.

How to improve backup

Always keep a secondary DNS server and keep a higher Expiry value. This will mean that even if the Primary server goes down, the secondary will have the cached copy(for as long as the Expiry value stands) and it will keep serving lookups. Keeping a secondary server but a low expiry value defeats the purpose of a Backup.

How to test SOA records

You have set the new SOA values, and you want to know whether the update has taken place. “Dig’’ is a good tool to troubleshoot and check for DNS information.

For example to check out the SOA records of yahoo.com from all the nameservers, primary and secondary, all you need to do is

# dig google.com +nssearch

SOA ns1.sgugal.com. root.manou.sgugal.com. 2006072101 28800 7200 3600 86400 from server ns2.sgugal.com in 1 ms.

SOA ns1.sgugal.com. root.manou.sgugal.com. 2006072101 28800 7200 3600 86400 from server ns1.sgugal.com in 28 ms.

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Exim Command Basics

Posted on December 25th, 2006 by Alex P..
Categories: Cpanel Hosting, Linux, web Hosting, EXIM, VPS / OpenVZ.

Message-IDs and spool files

The format of the message ID is three groups of base 62 digits, separated by hyphens. and take the form of: XXXXXX-YYYYYY-ZZ. The first group, of six digits, gives the integral number of seconds since the epoch. The second group, also of six digits, gives the process ID. The third group, of two digits, gives the fractional part of the number of seconds since the epoch, in units of 1/2000 of a second (500 us). The function does not return until the clock has advanced far enough that another call would generate a different ID.

Logs Files

Files in /var/spool/exim/msglog contain logging information for each message and are named the same as the message-id.

Files in /var/spool/exim/input are named after the message-id, plus a suffix denoting whether it is the envelope header (-H) or message data (-D).

Basic information

Print a count of the messages in the queue:

root@ashok# exim -bpc

Print a listing of the messages in the queue (time queued, size, message-id, sender, recipient):

root@ashok# exim -bp

Print a summary of messages in the queue (count, volume, oldest, newest, domain, and totals):

root@ashok# exim -bp | exiqsumm

Print what Exim is doing right now:

root@ashok# exiwhat

Run a pretend SMTP transaction from the command line, as if it were coming from the given IP address. This will display Exim’s checks, ACLs, and filters as they are applied. The message will NOT actually be delivered.

root@ashok# exim -bh 192.168.11.22

Display all of Exim’s configuration settings:

root@ashok# exim -bP

Searching the queue with exiqgrep

Exim includes a utility that is quite nice for grepping through the queue, called exiqgrep.

First, various flags that control what messages are matched. These can be combined to come up with a very particular search.

Use -f to search the queue for messages from a specific sender:

root@ashok# exiqgrep -f [luser]@domain

Use -r to search the queue for messages for a specific recipient/domain:

root@ashok# exiqgrep -r [luser]@domain

Use -o to print messages older than the specified number of seconds. For example, messages older than 1 day:

root@ashok# exiqgrep -o 86400 […]

Use -y to print messages that are younger than the specified number of seconds. For example, messages less than an hour old:

root@ashok# exiqgrep -y 3600 […]

Use -s to match the size of a message with a regex. For example, 700-799 bytes:

root@ashok# exiqgrep -s ‘^7..$’ […]

Use -z to match only frozen messages, or -x to match only unfrozen messages.

There are also a few flags that control the display of the output.

Use -i to print just the message-id as a result of one of the above two searches:

root@ashok# exiqgrep -i [ -r | -f ] …

Use -c to print a count of messages matching one of the above searches:

root@ashok# exiqgrep -c …

Print just the message-id of the entire queue:

root@ashok# exiqgrep -i

Managing the queue

The main exim binary (/usr/sbin/exim) is used with various flags to make things happen to messages in the queue. Most of these require one or more message-IDs to be specified in the command line, which is where `exiqgrep -i` as described above really comes in handy.

Start a queue run:

root@ashok# exim -q -v

Start a queue run for just local deliveries:

root@ashok# exim -ql -v

Remove a message from the queue:

root@ashok# exim -Mrm message-id [ message-id … ]

Freeze a message:

root@ashok# exim -Mf message-id [ message-id … ]

Thaw a message:

root@ashok# exim -Mt message-id [ message-id … ]

Deliver a message:

root@ashok# exim -M message-id [ message-id … ]

Force a message to fail and bounce as “cancelled by administrator”:

root@ashok# exim -Mg message-id [ message-id … ]

Remove all frozen messages:

root@ashok# exiqgrep -z -i | xargs exim -Mrm

Remove all messages older than five days (86400 * 5 = 432000 seconds):

root@ashok# exiqgrep -o 432000 -i | xargs exim -Mrm

Freeze all queued mail from a given sender:

root@ashok# exiqgrep -i -f luser@example.tld | xargs exim -Mf

View a message’s headers:

root@ashok# exim -Mvh message-id

View a message’s body:

root@ashok# exim -Mvb message-id

View a message’s logs:

root@ashok# exim -Mvl message-id

Add a recipient to a message:

root@localhost# exim -Mar message-id
 [ address … ]

Edit the sender of a message:

root@localhost# exim -Mes message-id  address

Searching the logs with exigrep

The exigrep utility (not to be confused with exiqgrep) is used to search an exim log for a string or pattern. It will print all log entries with the same internal message-id as those that matched the pattern, which is very handy since any message will take up at least three lines in the log. exigrep will search the entire content of a log entry, not just particular fields.

One can search for messages sent from a particular IP address:

root@ashok# exigrep ‘<= .* [12.34.56.78] ' /path/to/exim_log

Search for messages sent to a particular IP address:

root@ashok# exigrep ‘=> .* [12.34.56.78]’ /path/to/exim_log

This example searches for outgoing messages, which have the “=>” symbol, sent to “user@domain.tld”. The pipe to grep for the “<=" symbol will match only the lines with information on the sender - the From address, the sender's IP address, the message size, the message ID, and the subject line if you have enabled logging the subject. The purpose of doing such a search is that the desired information is not on the same log line as the string being searched for.

root@ashok# exigrep ‘=> .*user@domain.tld’ /path/to/exim_log | fgrep ‘<='

Generate and display Exim stats from a logfile:

root@ashok# eximstats /path/to/exim_mainlog

Same as above, with less verbose output:

root@ashok# eximstats -ne -nr -nt /path/to/exim_mainlog

Same as above, for one particular day:

root@ashok# fgrep YYYY-MM-DD /path/to/exim_mainlog | eximstats

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What is OpenVZ ?

Posted on October 1st, 2006 by Admin.
Categories: web Hosting, VPS / OpenVZ.

OpenVZ is an Operating System-level server virtualization solution, built on Linux. OpenVZ creates isolated, secure virtual environments — VEs (otherwise known as virtual private servers, or VPSs) on a single physical server enabling better server utilization and ensuring that applications do not conflict. Each VPS performs and executes exactly like a stand-alone server; VPSs can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. See Documentation at http://openvz.org/documentation/tech/ for more information.

The OpenVZ project is an open source community project supported by SWsoft and is intended to provide access to the code and ultimately for the open source community to test, develop and further the OS virtualization effort. It is also a proving ground for new technology that may evolve into the Virtuozzo product offering. We encourage the community to access, use, develop and comment on the software and references on this site.

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